Broadly, solar energy collecting systems include a collecting means which receives the solar energy and converts it to a useful form. In most energy collecting systems a receiving, focusing or reflecting means of some type receives the sun's rays from a predetermined extended area and directs the received solar energy to a collector means of some type which, in turn, receives the initial energy in an enhanced or concentrated form, specifically at a much higher degree of heat per unit area than originally received by the receiving means. The collector means utilizes the energy which it receives to heat a fluid, such as air or water, directly for immediate use or stores the same in a heat sump or heat reservoir for ultimate use on demand. The heat energy received by the collector may also be converted to electrical energy for immediate use or converted to electrical energy and stored in storage devices or batteries for ultimate use on demand.
Most solar energy systems, in use or proposed for use, have been of the type in which an extended reflecting surface receives the solar energy and directs it to a substantially smaller collector means. Such reflecting surfaces may also take a wide variety of forms. For example, flat, dished, parabolic troughs, etc. The system may also be of the tracking or nontracking type, which, to a great extent, depends upon the receiving surface. For example, flat receiving surfaces or reflecting surfaces need to be oriented at all times according to the position of the sun in order to receive sufficient energy. Thus, such systems are so-called tracking systems when the receiving surface tracks the movement of the sun from horizon to horizon on a daily basis and, preferably, the azimuthal position of the sun on a seasonal basis. While tracking on a seasonal basis can be performed manually, it is wholly impractical to manually track the sun on a daily basis. Accordingly, automatic tracking systems are provided. Such tracking systems are complex and expensive to operate and maintain. By contrast, a parabolic trough-type receiving means can be utilized as a so-called nontracking system. By appropriately shaping the parabola, sizing and positioning a collector within the parabola so as to receive substantially all of the energy striking and reflected by the inner reflecting surface of the parabola and correctly positioning the reflector surface in a generally east-west direction, it is unnecessary to track on a daily basis and all that is required for maximum efficiency is changing the orientation several times, for example, two to four times per year, to accommodate seasonal changes of the positions of the sun.
The collector means for solar energy systems either receives solar rays directly, or as previously pointed out, indirectly from a receiving, focusing or reflecting means. The basic component of the collecting means comprises an absorber means which is generally a panel or plate-type device adapted to absorb the collected solar energy and convert it to an immediately useful form or a form which can be stored for use on demand. For this purpose, the absorber means is constructed of a material adapted to absorb the heat and, to the extent possible, retain the absorbed heat, often being a black body or a body having a coating of black paint as opposed to a reflective body. In a majority of instances the absorber means is a flat plate-type heat exchanger. Heat exchange is carried out by forming fluid passages such as rectangular ducts, tubular ducts and the like through which a heat exchange medium is flowed. In order to shield or insulate the exposed side or sides of the absorber means against heat losses through conduction and convection and/or cooling by the wind, it is conventional practice to mount a transparent plate or sheet adjacent the exposed side of the absorber plate and spaced therefrom so as to form an essentially dead air space between the absorber plate and the shielding plate. Thus, the shielding or insulating plate will transmit solar energy therethrough to the absorber plate, while at the same time preventing direct contact by the wind, and heat losses from the absorber plate by conduction and convection. Generally, the shielding or insulating plate is a polymeric material of some type such as polyethylene, polyvinylchloride, etc. and may be in the form of a rigid or semirigid plate or a flexible sheet material. Regardless of the structure of the shielding or insulating panel or panels, the most serious problem encountered is rapid deterioration of the panels, usually because of the high degree of heat concentrated in the absorber plate and the mounting which requires some connection between the absorber plate and the shielding panel. Thus, there is the need for frequent replacement. Hence, it is necessary that the shielding or insulating panel be mounted so as to not contact the absorber plate. However, regardless of the manner of mounting, there is still the problem of the shielding panel eventually deteriorating and requiring replacement because of radiated heat and conducted heat through the connecting means. This is particularly true in the case of panels of flexible polymeric materials. While such panels are usually stretched taut and are often of material which will shrink to thus further tighten the same, there is still a tendency for the wind to force the material into contact with the absorber plate or for the material to lose its resiliency and sag into contact with the absorber plate. Thus, it is highly desirable that some means of maintaining the shielding or insulating panel, often referred to as "glazing", relatively cool, preventing contact with the absorber plate and providing some means for rapidly replacing deteriorated panels.